<?php

// Enter your code here, enjoy!

$str = '10100111001';
$state = 'neutral';
$ups = true;
$level = 0;

for ($i = 0; $i < strlen($str); $i++)
	{
	echo $str[$i] . ': ';
	if ($str[$i] == '1' && $ups === true && $level == 0)
		{
		echo 'case 1 ';
		$step[] = 'U';
		$level = 1;
		$ups = false;
		continue;
		}

	if ($str[$i] == '1' && $ups === false && $level == 1)
		{
		echo 'case 2 ';
		$step[] = 'D';
		$level = 0;
		continue;
		}

	if ($str[$i] == '1' && $ups === false && $level == 0)
		{
		echo 'case 3 ';
		$step[] = 'D';
		$level = - 1;
		$ups = true;
		continue;
		}

	if ($str[$i] == '1' && $ups === true && $level == - 1)
		{
		echo 'case 4 ';
		$step[] = 'U';
		$level = 0;
		continue;
		}

	if ($str[$i] == '0')
		{
		echo 'case 6 ';
		$step[] = 'n';
		continue;
		}
	}

function build($prev, $cur, $next)
	{
	if ($prev == 'n' && $cur == 'n' && $next == 'n')
		{
		echo border
		}
	}

echo count($step);
echo "\n";

for ($i = 0; $i < count($step); $i++)
	{
	if ($i != 0)
		{
		$step[$i];
		}
	}